Direct current power supplies are generally designed for optimum performance in a constant voltage mode (CV) or in a constant current mode (CC). In either case there is a "limit" mode of operation at which the supply automatically switches from one mode to the other. Specifically when a constant voltage supply, CV, reaches a current output such that CV/CC.gtoreq.RL, wherein CV is the constant voltage setting , CC is the constant current setting and RL=the load resistance, it switches into a constant current mode and when a constant current supply reaches a current such that CV/CC.gtoreq.RL, it switches to a constant voltage mode.
A power supply optimized for CV operation should approach zero output impedance at all frequencies, and a power supply optimized for CC operation should approach an infinite output impedance at all frequencies.
A power supply optimized for CV operation generally has a large output capacitor connected between its output terminals that minimizes the output impedance for the CV mode but impairs its transient response for varying loads when operating in a CC mode.
A power supply optimized for CC operation usually does not have an output capacitor connected between its output terminals, but the lack thereof causes a poorer load effect transient response when operating in CV mode.